histedit: byteify the help for the multifold action
While there's some allowance for str in `_()`, it's commented to be for "goofy
unicode docstrings in test", so no idea how well that works, but it should at
least come back as bytes. With HGPLAIN, however, the str isn't touched and is
returned as-is, so this seems like a real bug.
#require docutils gettext
$ $TESTDIR/check-gendoc fr
checking for parse errors